pylint: Set a minimum duplicate match to 10 lines.

This patch adjusts pylint to disregard duplicate matches
for up to 10 lines.

The number is chosen to permit overriding with up to
3 identical lines for `def arguments(self)` and
`def result(self)` while two more lines for `arity`
and `input_style` in the bignum test suite.

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>

.pylintrc

@@ -1,5 +1,6 @@
 [MASTER]
 init-hook='import sys; sys.path.append("scripts")'
+min-similarity-lines=10
 
 [BASIC]
 # We're ok with short funtion argument names.